Ultrasound diagnosis apparatus acquires biological information of a subject by sending ultrasound waves into the subject and receiving reflected waves through an ultrasound probe. The ultrasound diagnosis apparatus then generates ultrasound image data, which represent, for example, tissue structures of the subject, based on the acquired biological information.
As for prior-art ultrasound diagnosis apparatuses, there is a technique known as “transmission-reception compound technique”. The transmission-reception compound technique is a technique in which ultrasound waves through the subject are transmitted and received based on a plurality of transmission and reception conditions, and a plurality of sets of image data obtained accordingly are then combined to generate composition image data. For example, an ultrasound diagnosis apparatus transmits and receives ultrasound waves through the subject in a plurality of transmission and reception directions as transmission and reception conditions and then combines a plurality of sets of image data thus obtained. In addition, the ultrasound diagnosis apparatus may transmit and receive ultrasound waves of a plurality of transmission and reception frequencies through the subject as transmission and reception conditions and then combine a plurality of sets of image data thus obtained. Furthermore, the ultrasound diagnosis apparatus may generate a set of image data for each of a plurality of received-signal processing conditions as transmission and reception conditions and may combine a plurality of sets of image data thus obtained.
In such a transmission-reception compound technique, for example, the ultrasound diagnosis apparatus calculates arithmetic means for the pixel values of a plurality of sets of image data to determine pixel values for composition image data so as to generate the composition image data with reduced speckle noise.
Moreover, by the transmission-reception compound technique, the ultrasound diagnosis apparatus may emphasize a particular tissue structure depicted in an image. In such a case, the ultrasound diagnosis apparatus selects maximum values from the pixel values of a plurality of sets of image data and sets the maximum values as pixel values for composition image data so as to generate the composition image data with an enhanced contour for the tissue structure depicted in an image. In the specification, this method of image-synthesis is referred to as “highest selection”.
However, the image generated through the arithmetic means as composition image data has been such that the difference in pixel values representing the contour and the other part is smaller than that of the image generated through the highest selection as composition image data. As a result, the image generated through the arithmetic means as composition image data is rather difficult for the user to visually recognize the contour. On the other hand, the composition image data generated through the highest selection include more speckle noise than the composition image data generated through the arithmetic means. This means that images from the composition image data generated through the highest selection show unevenness in pixel values for the same tissue. Accordingly, the images are difficult for the user to visually recognize the same tissue.